This invention relates to antennas, phased array antennas, and specifically to a multi-band, wide-angle scan, and narrow beamwidth phased array antenna with grating lobe suppression.
Over the last four decades, much effort has been given to the development of methods to scan reflector antennas through large angles. Techniques for shaping the reflector to compensate for the distortion caused by scanning have been investigated as disclosed in “Wide-Angle Scanning with Reflector Antennas: a New Design Technique”, IEEE National Aerospace and Electronics Conference, 2000, pp. 136–145. The technological challenges to cancel sidelobes and suppress clutter are known.
Previous attempts to provide antennas with multi-band wide-angle scan capabilities have included passive interlaced arrays where two antenna arrays of some type on different bands are assembled together or interlaced to reduce size. Interlaced arrays are limited in the number bands of operation where three and four band operation needed for current applications is difficult to obtain. Antennas employing reflector technology such as parabolic reflectors are difficult to implement in multiple bands. Furthermore, such antennas typically have slow mechanical beam scanning making it difficult to track a communications satellite in a rapidly maneuvering vehicle. Lens antennas are difficult to implement in multi-band designs. A three or more band configuration requires different focal points.
A phased array antenna is a beam forming antenna in which the relative phases of the respective signals feeding the antennas are varied such that the effective radiation pattern of the phased array is reinforced in a desired direction and suppressed in undesired directions. The relative amplitudes of constructive and destructive interference effects among the signals radiated by the individual antennas determine the effective radiation pattern of the phased array. A phased array may be used to rapidly electronically scan in azimuth or elevation. Previous phased arrays have been limited in bandwidth.
Ultra broadband radiating elements in conventional phased array antennas initiate grating lobes. Grating lobes are referred to as secondary maxima that appear with the main beam of the phased array antenna along the visible region. A grating lobe impacts the phased array antenna by dividing transmitted and received power into false and main beams. The grating lobe provides ambiguous directional information from that associated with the main beam.
Efficient broadband radiating elements tend to be large thereby making an entire phased array too large for many applications. Excessively large radiating element size forces a wide element-to-element spacing within a phased array that generates grating lobes at the high end of the bandwidth.
What is needed is a phased array antenna system with wide-angle scanning and simultaneous multi-beam multi-band operation without undesired grating lobes.